Fossil diatoms (Renkum) in darkfield.

WalterD · Post by **WalterD** » Tue Apr 23, 2019 7:09 am

Diatoms can be found in water...but also in the soil. With a lot of help I succeeded making a permanent mount of such a (cleaned) sample in Pleurax. Pleurax is a mounting medium with a very high refractive index-1.73-, similar like Zrax and Naphrax.
In Holland, diatomaceous earth has virtually disappeared, through the years it has been used for production of e.g. dynamite, toothpaste and for filtration. Therefore very nice to look at this Renkum sample. Because Renkum is kind of famous, the diatoms are quite easy to identify, I found:

1. Epithemia turgida
2. Pinnularia nobilis
3. Pinnularia nobilis
4. Gomphonema acuminatum
5. Stauroneis phoenicenteron
6. Cymbella cuspidata

All were taken with darkfield and a 100x iris objective. I wanted to use a 1,3 Na darkfield condenser but somehow this did not work. The 0.8 Na condensor was okay, of course the diaphragm in the objective had to be partially closed. You might have noticed picture 6 is inverted darkfield.

All and all many different fossil diatoms in this slide, this was just a small selection.

Saul · Post by **Saul** » Tue Apr 23, 2019 9:03 am

Walter, impressive set

#3 is my favorite

Jacek · Post by **Jacek** » Tue Apr 23, 2019 12:03 pm

SUPER !

Sumguy01 · Post by **Sumguy01** » Tue Apr 23, 2019 8:21 pm

Very nice set.
I like #5 best.
Thanks for sharing.

micro_pix · Post by **micro_pix** » Wed Apr 24, 2019 1:31 am

Very nice.

WalterD · Post by **WalterD** » Wed Apr 24, 2019 3:37 am

Thank you for your positive remarks, gentlemen.

I've added 6 more darkfield pictures today. Identification in progress.
Though there were hardly any damaged diatoms in the sample, I thought the one in the last picture was beautiful in its own way.

While I'm here I would like to use the opportunity to ask whether any forum members have experience with high power darkfield condensers that match with the ortholux II?
I own the one mentioned in below article
http://www.microscopy-uk.org.uk/mag/ind ... holux.html
This one has an Na 1.20 and as mentioned, it did not work in my setup.

But there also is one with a 1.20-1.44 Na top lens with the model number 513466. Maybe this one fits in condensers suitable for a different microscope model? Would like to know what it looks like.

zzffnn · Post by **zzffnn** » Wed Apr 24, 2019 6:51 am

Beautiful images, @WalterD! Thank you for sharing!

Did you do anything to reduce halos? I am surprised by how clean your images are, especially #1, #2, #3 and the very last one. Typical darkfield images (and halos) would look like photos #9 and #10 (counting from top to bottom, or #3 and #4 if you count backwards).

Technically, your photos #2, #3 and the last one is circular oblique light (COL) and not darkfield, because your objective iris was set wider than where darkfield stop occupies. Your photo #1 is more of a transition between darkfield and COL, leaning more into darkfield.

However you called it, you executed it very well and achieved fantastic imageries.

Many times COL images would look like your photo #4, which does not look as nice as as #2 and #3.

I have a Heine condenser adapted to my Nikon Optiphot, but don't like the halos it produces.

What did you mean when you said your NA 1.20 (or 1.30?) condenser "did not work"? Did you mean that it did not fit your scope?

micro_pix · Post by **micro_pix** » Wed Apr 24, 2019 8:47 am

Another lovely set of images.

iconoclastica · Post by **iconoclastica** » Wed Apr 24, 2019 9:51 am

This is impressive, Walter, you're way ahead of me...

I have never known they were found here. It's so close, I could even walk to it. Did you collect them yourself?

Wim

carlos.uruguay · Post by **carlos.uruguay** » Wed Apr 24, 2019 8:06 pm

A beauty!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

WalterD · Post by **WalterD** » Thu Apr 25, 2019 12:34 am

Update:

7 Surirella biseriata
8 Synedra pulchella
9 Aulacoseira crenulata
10
11 Epithemia turgida (2)
12 Pinnularia viridis & Pinnularia nobilis
13/14 Synedra acus

Thank you again, dear forum members. The image added today was done with differential interference contrast and a 63x/1.3 fluoreszenz objective, I switched over to darkfield after.

I have never known they were found here. It's so close, I could even walk to it. Did you collect them yourself?

No I did not find them, Wim. My friend Michel Haak had some in alcohol in stock. Michel is a master in cleaning, mounting and arranging diatoms and collects diatoms from all over the world. (see his work at www.diatoms.eu)
We made the mount together and thanks to his skills the slide quality is very good. Diatomaeceous earth is no longer available in Renkum as far as I know. If you pm me I can forward you the address of his diatom related webshop as well. Or is a bit of advertising allowed, moderator?

Did you do anything to reduce halos? I am surprised by how clean your images are, especially #1, #2, #3 and the very last one. Typical darkfield images (and halos) would look like photos #9 and #10 (counting from top to bottom, or #3 and #4 if you count backwards).

Zzffnn, The setup is the collector lens of an orthoplan lamphouse, with a Canon speedlite flash. For the whole set the setup was practically identical,
-aperture of the iris diaphragm
-height and centering of the 0.8 Na condenser
-intensity of the electronic flash was varied a bit
Furthermore the amount of pleurax between the coverslip and the diatom is minimal as result of the mounting technique.
What I did though was taking the pictures underexposed with the minimum required amount of light. When processing the raw files the blacks, whites, exposure, shadows, highlights etcetera were adjusted.
This flexibility is the reason why I always shoot in raw. Due to variations in postprocessing e.g. the background lightness comes out different. But the speedlite may also have been a tiny bit offcenter, if that would make a difference.

What did you mean when you said your NA 1.20 (or 1.30?) condenser "did not work"? Did you mean that it did not fit your scope?

The 1.20 condenser dovetail mount fits in the Ortholux II, I just could not produce a detailed halo-free image with double immersion in that setup.

JH · Post by JH » Sun Apr 28, 2019 2:55 am

Excellent and interesting pictures
Best regards
Jörgen Hellberg

iconoclastica · Post by **iconoclastica** » Sun Apr 28, 2019 3:34 am

I found a map showing the spot. If I can manage, I'll go there next week. I am not sure I can recognize the stuff, though. But even then it is a lovely area for a short cycle tour.

For what I read about it, the site has been quarried until all was taken. But there's a difference between completely gone and 'no longer economically profitable to recover'. So perhaps there's still a pinch to be found.

rjlittlefield · Post by **rjlittlefield** » Sun Apr 28, 2019 9:29 am

WalterD wrote:If you pm me I can forward you the address of his diatom related webshop as well. Or is a bit of advertising allowed, moderator?

Posting the link publicly would be fine.

--Rik

WalterD · Post by **WalterD** » Fri May 03, 2019 10:31 pm

Thank you Jörgen.

Glad that this thread is inspiring others to post new diatom pictures too.

Yes, if you're interested you should visit Michel's ebay store with lots of interesting diatoms:

https://www.ebay.nl/sch/diatoms-nl/m.ht ... pg=&_from=

And of course his webshop:

https://www.diatoms.nl/index.php

I found a map showing the spot. If I can manage, I'll go there next week. I am not sure I can recognize the stuff, though. But even then it is a lovely area for a short cycle tour.

That's impressive research, Wim. And also an extremely detailed report from the guy who wrote it, including depths and cosistency. I can imagine that diatomaceous earth is not evenly distributed, some spots may only have a few mm layer that is not profitable for "mining".
Did you find anything? Of course the next challenge will be chemically cleaning and concentrating the stuff..